What is Concrete: A combination of cement, water, fine aggregates (like sand), and coarse aggregates (like gravel or crushed stone) is used to make concrete, a common building material. It is a composite substance that hardens and solidifies after curing or setting.
The primary binder and key component of concrete is cement. Clay, limestone, and other materials are heated to high temperatures to create cement. Cement creates a paste when combined with water, which fuses the particles to form a solid mass.
Sand is a fine aggregate that fills in the spaces left by the bigger particles in the concrete mix and increases its workability. Gravel or crushed stone are examples of coarse aggregates that give concrete bulk and strength.
The chemical process known as hydration, which takes place when cement and water interact, requires water. Chemical compounds that harden and give concrete its strength are created by this process.
Concrete can support enormous weights and resist compression because it has good compressive strength. Additionally, it possesses strong resistance to corrosion, abrasion, and chemical assaults. Concrete is a versatile material utilised in a variety of construction applications, such as buildings, bridges, roads, dams, and more, thanks to these qualities.
Concrete is a versatile material for architectural and ornamental uses due to its ability to be moulded into a variety of forms and sizes in addition to its structural qualities. Concrete that has been reinforced can be made by adding steel bars or mesh to increase its strength.
GRADES OF CONCRETE
Based on its compressive strength—the capacity of concrete to bear loads or forces that tend to crush it—concrete is divided into several grades or classes. Concrete grades are frequently identified by a number, such as M20, M25, C30, etc. These figures indicate the typical compressive strength of concrete following a 28-day curing period.
- M5 grade: 5 megapascals (MPa), or 725 pounds per square inch (psi), is the typical compressive strength of concrete of the M5 grade. Typically, it is utilised for non-structural tasks like levelling beds, paths, etc.
- M10 Grade: M10 grade concrete has a typical compressive strength of 10 MPa (1450 psi). For non-structural uses like flooring, paths, etc., it is employed.
- M15 grade: Concrete of the M15 grade has a typical compressive strength of 15 MPa (2175 psi). Small domestic building projects like residential flooring, paths, etc. frequently employ it.
- M20 grade: Concrete of the M20 grade has a typical compressive strength of 20 MPa (2900 psi). It is extensively utilised in general construction, including the construction of foundations and small industrial and residential buildings.
- M25 grade: Concrete of the M25 grade has a typical compressive strength of 25 MPa (3625 psi). It is frequently used in commercial buildings, heavy-duty pavements, and medium-rise buildings.
- M30 grade: Concrete of the M30 grade has a typical compressive strength of 30 MPa (4350 psi). It is used to create bridges, tall buildings, and other constructions that call for a lot of strength.
- M40 grade: Concrete of the M40 grade has a typical compressive strength of 40 MPa (5800 psi). Heavy-duty buildings like bridges, retaining walls, and foundations frequently utilise it in their construction.
These are but a few illustrations of the many grades of concrete. The unique needs of the construction project, such as the anticipated loads, environmental factors, and design considerations, will determine the concrete grade to be used. To maintain the structural integrity and endurance of the structure, engineers and architects base their choice of concrete grade on these considerations.
TYPES OF CONCRETE
Plain Concrete
The most fundamental kind of concrete, sometimes referred to as regular concrete. In order to make it, cement, aggregates, and water are combined. There are no reinforcements or additions in it. For non-structural applications including sidewalks, driveways and flooring, plain concrete is frequently employed.
Reinforced concrete
Steel reinforcement bars (rebars) or a steel mesh placed into the concrete make up reinforced concrete, a composite material. The reinforcing gives the concrete tensile strength, increasing its ability to support structures and reducing the likelihood of cracking. Building foundations, columns, beams, slabs, and other structural components frequently employ reinforced concrete.
Prestressed concrete
Concrete that has been pre-compressed or strained to counteract the tensile stresses that develop when it is loaded is known as “prestressed concrete.” The pre-stressing procedure contributes to the concrete’s increased strength and durability. In applications where long spans and large load capacities are necessary, such as bridges, high-rise structures, parking structures, etc., prestressed concrete is frequently employed.
Lightweight Concrete
To create lightweight concrete, expanded clay, shale, or perlite are used in place of part or all of the usual aggregates (such as gravel or stone). Because of the lesser density of this form of concrete, it is lighter. In situations where weight reduction is desired, such as in precast concrete components, insulating panels, and buildings with lower dead loads, lightweight concrete is employed.
High-Strength Concrete
Compared to regular concrete, high-strength concrete is intended to have a greater compressive strength. It is accomplished by using high-quality aggregates, a lower water-to-cement ratio, and frequently adding admixtures. Tall buildings, bridges, and large industrial complexes all demand enhanced load-bearing capability, hence high-strength concrete is employed in these types of constructions.
Self-Consolidating Concrete
Self-Consolidating Concrete (SCC) is very flowable and doesn’t require mechanical consolidation. It is sometimes referred to as self-leveling concrete. Without the need for vibration, it may flow and fill the formwork under its own weight, guaranteeing homogeneous compaction. Architectural components and strongly reinforced structures are two examples of applications where SCC is frequently utilised. These applications involve complicated geometries and crowded reinforcement.
Coloured concrete
Concrete that has been coloured can be made by adding pigments or dyes into the concrete mixture. When a certain aesthetic look or colour scheme is needed, this sort of concrete is employed. Landscape uses, ornamental pavements, and architectural projects all frequently employ coloured concrete.
WHAT IS DESIGN MIX CONCRETE
A form of concrete where the proportions of its component ingredients are specified and created to suit precise strength and durability criteria for a particular project is known as design mix concrete, also known as controlled mix concrete or proportional concrete. To guarantee that the finished concrete has the appropriate qualities, the design mix is created using mathematics and laboratory tests.
The processes that are normally taken to make design mix concrete are as follows:
Determines the specifications
The engineer or designer determines the specifications for the concrete, including the intended compressive strength, workability, durability, and any other project-specific needs.
Material Selection
The right cement, aggregates (such sand and coarse aggregates), water, and other necessary admixtures are selected for the concrete mixture. The components must adhere to all applicable norms and requirements.
Proportion
The ratios of the elements are chosen depending on the qualities of the available resources and the desired attributes of the concrete. This entails figuring out how much cement, aggregates, and water are needed to create the desired mix design.
Mix Design
The mix design process involves experimenting with different material combinations and figuring out the best ratios to achieve the required concrete qualities. To assess and improve the mix design, laboratory procedures including slump tests and compressive strength testing are carried out.
Trial Batches
Following the completion of the mix design, concrete is made and tested in trial batches to ensure that the appropriate qualities are obtained. If required, adjustments can be made to perfect the combination.
Manufacturing and Quality Control
Following the prescribed proportions and processes, concrete manufacturing starts when the design mix has been authorised. In order to maintain consistency and conformity with the design mix, quality control methods are put into place throughout batching, mixing, and placing.
Contrary to nominal mix concrete, which has undefined material proportions, design mix concrete has advantages. Engineers may precisely control the concrete’s performance characteristics, such as strength, durability, workability, and resistance to environmental conditions, by carefully planning the mix.
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WHAT IS NOMINAL MIX CONCRETE
Nominal mix concrete is a form of concrete in which, as opposed to precise calculations, the ratios of its component components are defined using approximate ratios or volume-based measures. Since the proportions are presented in terms of usual measurements or ratios, the focus in nominal mix concrete is on simplicity and usability.
For instance, a typical nominal mix for concrete is 1:2:4, which equals one component cement, two parts fine aggregates (like sand), and four parts coarse aggregates (like gravel or crushed stone). These ratios are regarded as a general starting point for mixing the concrete.
Mix nominally In small-scale building projects or circumstances where exact control over the concrete mix is not essential, concrete is frequently utilised. For non-structural components like passageways, tiny foundations, or low-stress applications, it could be appropriate.
It’s crucial to remember that nominal mix concrete does not offer perfect control over the concrete’s characteristics. As the actual qualities rely on elements including the quality and properties of the materials used, the water-cement ratio, and the degree of compaction during installation, it can lead to variances in strength, workability, and durability.
It is advised to utilise design mix concrete in instances when specified concrete qualities and performance criteria are essential, such as in structural elements or high-stress applications. In order to calculate the amounts of elements that will produce the appropriate qualities and adhere to the project’s requirements, design mix concrete requires exact calculations and laboratory testing.
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MINIMUM AND MAXIMUM SETTING TIME OF CONCRETE
The duration it takes for the concrete mixture to transition from a liquid, working condition to a solid state is referred to as the setting time of concrete. It is a crucial characteristic that influences how concrete is handled, placed, and finished. The kind of cement used, the water-cement ratio, the temperature, and the admixtures all have an impact on the setting time.
Initial Setting Time
The initial setting time is the amount of time required for concrete to transition from a fluid condition to a state in which it can hold a weight without experiencing considerable distortion. The majority of concrete combinations have a minimum first setting time of around 30 minutes, therefore the concrete should become sufficiently firm within this period.
Final Setting Time
The final setting time is when the concrete has fully hardened and is strong enough to withstand minor surface abrasions. The majority of concrete combinations have a minimum final setting time of 1.5 to 2 hours, however this might vary based on the unique circumstances.
It’s crucial to remember that a variety of factors might affect how quickly concrete sets. For instance, greater temperatures have a tendency to hasten the setting time whereas lower temperatures might have the opposite effect. Depending on the needs of the project, mixes like accelerators or retarders can also be employed to change the setting time.
STRENGTH OF CONCRETE
Concrete’s strength is a crucial characteristic that affects its capacity to bear applied weights and resist deformation. The strength of concrete varies depending on its grade, and it is commonly expressed as compressive strength. Standardised tests are used to ascertain the compressive strength of concrete, generally after 28 days of curing.
M5 Grade: M5 grade concrete typically has a compressive strength of 5 MPa (725 psi).
M10 grade: Concrete of the M10 grade usually has a compressive strength of 10 MPa (1450 psi).
M15 grade: Concrete of the M15 grade typically has a compressive strength of 15 MPa (2175 psi).
M20 grade: Concrete of the M20 grade usually reaches a compressive strength of around 20 MPa (2900 psi).
M25 grade: Concrete of the M25 grade has a compressive strength of around 25 MPa (3625 psi).
M30 grade: Concrete of the M30 grade typically has a compressive strength of 30 MPa (4350 psi).
M40 Grade: Concrete of the M40 grade typically has a compressive strength of 40 MPa (5800 psi).
For specialised applications requiring particularly high strength, such as in large industrial structures or infrastructure projects, higher-grade concretes, such as M50 and above, are also employed.
It is crucial to keep in mind that these figures are approximations and may change based on the calibre of the employed materials, the water-to-cement ratio, the curing circumstances, and the particular mix design.
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